The invention relates to a propelling nozzle and, more particularly, to a propelling nozzle having a variable course of the nozzle contour for flight aggregates operated in the subsonic, supersonic and hypersonic range.
The nozzle has upper and lower primary and secondary flaps which are disposed opposite one another at a mutual distance and which are sealingly movably guided between lateral wall portions of a four-cornered nozzle housing. The primary flaps are arranged pivotally about a fixed axis of rotation on the nozzle housing. The secondary flaps, in each case upstream of levers non-rotatably connected with the primary flaps, are pivotally linked to pivots situated on the side facing away from the nozzle flow. The secondary flaps change into the primary flaps with a surface section which is bent concentrically with respect to the pivots. The propelling nozzle is arranged between the jet pipe of a turboramjet engine and a radially exterior expansion ramp of the flight aggregate.
Recently, combined turboramjet engines, among others, have regained importance, specifically within the scope of so-called "hypersonic flight concepts" having a extremely high spectrum of application from the start to the high supersonic speed at high flight altitudes, e.g. up to an altitude of approximately 30 km. In this case the "hypersonic flight concepts" includes among other things a space flight aggregate concept, i.e. the "Sanger" Project which amounts to a two-stage concept, as described in the following. The first stage is to be carried out by a flight aggregate operating only within the atmosphere, while the second stage is based on a useful-load flight aggregate which is taken along "piggyback" by the mentioned flight aggregate and which, for the purpose of space mission, in the upper range of the atmosphere, by means of a suitable rocket propulsion system, is to independently continue on the flight path assigned to it. The flight aggregate responsible for the first stage can therefore return and be reused. The flight aggregate carries out starts and landings like a conventional airplane.
In the case of combined turboramjet engines which are to be used, for example, for a flight aggregate of this type, generally, when a flying speed of approximately Mach 3 is reached, the turbojet engine is to be switched off continuously, and the respective ramjet propulsion is to be switched on continuously. Thus, by means of the ramjet propulsion alone, desired high supersonic or hypersonic speeds are reached of up to Mach 4.5 or even more. Flying speeds of approximately Mach 2 or even more may be achieved in this case in the combined operation of "jet engine with a switched-on afterburner". The afterburner, which for this purpose is advantageously connected behind the jet engine part, is possibly acted upon by a combination of compressor or fan air and engine exhaust gas. The afterburner, by means of the connection of additional fuel injection devices together with flame stabilizers, may form the propulsion system for the ramjet operation, with a correspondingly proportioned exclusive ambient-air supply when the turbojet engine part is switched off.
In view of the above-mentioned extremely different flying, performance and ambient conditions, it is difficult to provide a propelling nozzle configuration by means of which essentially the following criteria must be brought into accord economically and optimally with respect to performance.
First, adaptation of the nozzle throat cross-section area (narrowest cross-section) to given, possibly extremely variable mass flows in the case of a flow Mach number (M.about.)=1 which can be adjusted in the plane of cross-section of the nozzle throat. This measure is necessary in the case of variable mass flows in order to always ensure the formation of a supersonic flow in the expansion part of the propelling nozzle.
Second, losses of flow energy or aerodynamic losses, as a result of the nozzle adjustment, must be kept low. The required variability of the nozzle contour course must be designed such that it will cause no compression surges in the supersonic flow.
Third, particularly in view of the extremely different flight altitudes, the course of the nozzle flow, and thus the nozzle outlet pressure, should be adaptable to the respective existing ambient condition (ambient pressure) in a manner that is optimal with respect to the propulsion.
Fourth, adjusting devices must be as few as possible--as well as energy expenditures for the required variations of the contour course of the propelling nozzle that are as low as possible.
The propelling nozzle concepts already suggested cannot, or only in an extremely insufficient manner, meet, in particular, the demands of an adaptation with lower flow energy losses to an extremely varying spectrum of ambient pressures in combination with an extremely high variation of the nozzle throat cross-section (narrowest cross-section variation up to 1:5 or even more).
In this context, reference should be made, for example, to a propelling nozzle concept which consists of an axially displaceable mushroom-shaped central body. The central body is axially symmetrically connected in the axial direction behind the afterburning and supplementary burning device of the combined turboramjet engine. In this case, the central body must be movable with respect to a cylindrical, stationary, convergently/divergently extending outer contour of the nozzle. The central body represents an aerodynamic interference body which is extremely thermally stressed and endangered by burn-up. A `free` hot-gas mass flow, which is required in view of the afterburning and supplementary burning (ramjet operation), cannot be ensured in this manner.
A comparatively complex flap-type double propelling nozzle concept has also been suggested with a view to an engine concept in which a ramjet combustion chamber which has its own propelling nozzle and can be connected separately is to be arranged above a disconnectable jet engine unit with an afterburner. A combined propelling-nozzle adjusting requirement, among others, in the case of only one nozzle, is not met in this case for the subsonic, supersonic and hypersonic operation. The latter also applies in connection with a propelling nozzle known from the German Patent Document DE-OS 31 21 653 in which, between straight walls which project axially on the side of the engine cell and are open laterally on the top and bottom, primary flaps are provided which can be swivelled around transverse axes and, at the extreme ends of which, unsupported secondary flaps, which can be swivelled about additional axes of rotation, form the respective divergent end part of the nozzle. The primary flaps which, in this case are opposite one another, essentially jointly form the convergent nozzle contour course including the respectively narrowest point (throat cross-section). In this case, among other things, special covering flaps are required which, on the exterior, must extend over the respective primary and secondary flap pairs, for the purpose of guiding ambient air which, if possible, should be aerodynamically surface-covering. In addition, by means of the variable swivelling capacity of the nozzle flaps, an exhaust gas shut-off should be possible within limits by means of the essentially axially symmetrical surface-covering contacting of the secondary flaps (thrust reversal operation) or a propulsion jet swivelling should be possible in a perpendicular plane. In addition, the primary and secondary flaps, by way of torsion waves--guided through the nozzle side walls--are to be adjusted. This adjusting requires laterally projecting aerodynamically unfavorable adjusting device application points and arrangements. In addition, in the known case, each primary and secondary flap of the propelling nozzle requires a separate adjusting drive. Because of the adjusting kinematics selected in the known case, it should also be difficult to be able to control, in an operationally safe manner, the gas forces affecting the primary and secondary flaps. This is true particularly in relation to the outside ambient pressure conditions.
U.S. Pat. No. 2,889,576 relates to a propelling nozzle for gas turbine jet engines having upper and lower primary and secondary nozzle flaps between lateral wall portions of a nozzle housing. The nozzle is constructed to be open on the top and on the bottom and has a variable nozzle contour (convergence, divergence or narrowest cross-section). The adjustment of the nozzle flaps takes place in interaction with respective radially outside upper and lower covering flaps. In adaptation to given mechanical variations of the convergent/divergent interior contour and of the narrowest cross-section, the covering flaps are spoilers which can be moved against the outside air flow. The lever adjusting kinematics and arrangement must mainly be constructed in such a manner that despite the differently adjusted nozzle divergence or divergence/convergence and deviating narrowest cross-section (prolate flap position, narrowest cross-section and outlet cross-section maximally opened), the covering flaps form a housing closure which, if possible, should be connected with low aerodynamic losses. In the known case, the primary flaps form, at the same time, thin covering elements of levers which are arranged at a radial distance to the levers and can be swivelled with the levers. The levers and the primary flaps can be swivelled by means of a separate adjusting drive by way of a front pivot on a radially upper part of the nozzle housing in order to adjust the respective narrowest cross-section by means of the primary flaps (convergent nozzle part). When the narrowest cross-section is adjusted, the nozzle divergence should then be separately adjustable by means of the secondary flaps starting from the covering flaps. In this case, the covering flaps can be swivelled by means of a separate adjusting drive about the pivot of the levers. In addition, by means of movably coupled intermediate levers, the covering flaps are longitudinally slidably and angularly adjustably coupled with the secondary flap end. By means of a flap end, which is symmetrically curved upstream toward an interior pivot, the secondary flaps are pivotally linked to the downstream ends of the levers and, from case to case, can be more or less moved into the primary flaps. A telescope-type spring-supported lever arrangement is provided between the interior pivot and the respective rear intermediate lever. A pivoted lever, which is supported on the housing side--in the vicinity of the pivot--acts upon the forward intermediate lever in an articulated manner.
The known propelling nozzles have several important disadvantages. These include high flap adjusting expenditures, particularly with respect to a combined nozzle/spoiler adjustment; predominantly one-sided flap support on the housing; special closing requirements of the nozzle housing, on the bottom as well as on the top; unstable housing construction, that is, the housing does not form a "pressure vessel" that is itself closed in so that considerable difficulties exist with respect to the establishment of a flap arrangement that is relieved from pressure; the extremely small throat cross-section and the relatively large expansion angle (secondary flaps in the case of a pronounced convergence) involve an exposure of the housing and a braking position ("spoiler"); a double adjusting drive is required for each set of primary and secondary flaps; the adjusting drive takes place laterally of the nozzle housing which, among other things, has an unfavorable influence on a structural arrangement of several engines together with the propelling nozzles next to one another that is densely crowded in the transverse direction; lateral weakening of the housing (adjusting drive); downstream ends of the primary flaps define the respective narrowest cross-section of the nozzle with an aerodynamically disadvantageous extreme edge overhang; with respect to stability, there is no clear "lever/primary flap" connection.
The British Patent Document GB-A 2098 280 relates to a two-dimensional convergent/divergent propelling nozzle for gas turbine engines which is variable with respect to its effective nozzle surface. The convergent/divergent nozzle, which is arranged in a four-cornered exhaust gas housing, consists of upper forward and rearward flaps, which interact with stationary upper and lower wall portions in the housing and are pivotally linked to one another. The nozzle also consists of a lower single flap which, on the interior side, is shaped convergently/divergently. In a combination of an axial displacement of the single flap, which takes place in the shape of a circular arc, and a buckling motion of the upper flaps, which takes place relative to it or to the nozzle axis, the interior contour of the nozzle can be varied with respect to the local axial displacement and change of the narrowest cross-section. In this case, the upper forward flap can be moved at the forward end, or both upper flaps can be moved at a joint pivotal linking point along curved guideways on the housing. In combination with a deflecting scoop for the jet deflection (vertical take-off or short take-off), which moves out downstream, together with an unfoldable fork, the smallest narrow surface of the nozzle must be formed between the maximally moved-out single flap (bottom) and the scoop. Separate driving devices are, in each case, assigned to the scoop, the two upper flaps and the single flap. In a variable nozzle end position, without jet deflection, the inner part of the unfoldable fork always forms an expansion section which geometrically continues the rearward upper flap.
From the British Patent Document GB-A-15 50 633, a combination is known of a convergently/divergently adjustable propelling nozzle with a jet reversing hood which can be moved downstream into the gas flow. The propelling nozzle consists of upper primary and secondary flaps which, on the housing of the combined device, engage in one another in a fork-shaped manner which compensates the adjusting path. The nozzle also consists of a radially downward flap which can be swivelled about a single axis of rotation. At the downstream upper end of the propelling nozzle, a control flap is provided for controlling the nozzle expansion angle or for influencing the flow-off direction of the propelling jet. The known case mainly relates to a supplying of cooling air to the propelling nozzle controlled by way of valves in a targeted manner. The cooling air is supplied in such a manner that a requirement-oriented cooling air supply should be possible while ensuring the local pressure differences for the supply (such as impact cooling) particularly in view of an optional cruise or V/STOL flight operation and the resulting pressure fluctuations in the exhaust gas jet. In the known case, a single pressure chamber for the fed cooling air is provided between the primary and secondary flaps and an arc-type exterior part of the nozzle housing. By way of openings, this chamber must be connected with cooling ducts integrated on the housing side.
This known case does not show any supply of boundary-layer air which is controlled by flaps--between the nozzle outlet and a stationary expansion ramp at the rear of the flight aggregate--for the purpose of an aerodynamic bounding of the propelling jet.
From U.S. Pat. No. 2,995,010, it is known to swivel, in the case of a propelling nozzle for gas turbine jet engines, the respective primary flaps by means of adjusting cylinders which act upon the flaps in the transverse direction, in an adaptation to the required nozzle convergence and the narrowest throat cross section. The adjusting cylinders, being pivotable at the extreme end, are anchored on an exterior supporting structure. In addition, the known case always requires a special adjusting lever control which is coordinated by way of a two-fold drive or a two-fold driven, mutually superimposed adjusting movement of the primary and secondary flaps and while applying an elastically deformable covering ring as the sealing device on the respective narrowest or buckling point between the two flap sets.
The French Patent Document FR-A-1588791 provides a secondary propelling nozzle which consists of flap elements which end in a wedge-shaped point. The flap elements can be moved axially and can be swivelled about transverse axes. The nozzle, in the case of a convergently/divergently adjusted nozzle contour course, by way of primary and secondary flaps, expanding in a ramp shape by means of the radially interior wedge surfaces, essentially connects to the downstream ends of the secondary flaps.
The PB 81-979485 reference shows a valve which is controlled via a locally measured pressure difference (sensor) information by way of an electronic engine control. The valve has the purpose of controlling the supply and the pressure of compressed air taken from the cyclic process in or into a pressure chamber which is constructed between interior flap structures (primary and secondary flaps) and exterior housing structures.
A multi-chamber system which is adapted to the locally graduated pressure course of the hot gas flow, with existing blocking-air differential pressures which are locally adapted with respect to the hot-gas flow at the most sensitive points (movable seals) is not shown in the mentioned case.
There is therefore needed a propelling nozzle which, as a supersonic expansion nozzle, makes it possible to achieve an aerodynamically advantageous adjustment of the nozzle throat cross-sectional surface over a wide operating range, without causing compression surges, in which case, the nozzle flow is to be adapted to a large ambient pressure rang (extremely different flight altitudes) in a propulsion-optimal manner.
These needs are met by the propelling nozzle according to the present invention having a variable course of the nozzle contour for flight aggregates operated in the subsonic, supersonic and hypersonic range. The nozzle has upper and lower primary and secondary flaps which are disposed opposite one another at a mutual distance and which are sealingly movably guided between lateral wall portions of a four-cornered nozzle housing. The primary flaps are arranged pivotally about a fixed axis of rotation on the nozzle housing. The secondary flaps, in each case upstream of levers non-rotatably connected with the primary flaps, are pivotally linked to pivots situated on the side facing away from the nozzle flow. The secondary flaps change into the primary flaps with a surface section which is bent concentrically with respect to the pivots. The propelling nozzle is arranged between the jet pipe of a turboramjet engine and a radially exterior expansion ramp of the flight aggregate. The primary and secondary flaps are arranged in a four-cornered nozzle housing which is itself closed in. In each case the secondary flaps are arranged on the nozzle housing in an axially movable and angularly adjustable manner at the downstream end. The levers are formed on interior sections which are bent away from the primary flaps in a toggle-lever-type manner. At the rearward ends of the levers, pivots are located. The levers have cutouts which are concentric with respect to the pivots. The surface sections of the secondary flaps can be moved into the cutouts. The upper and the lower primary and secondary flaps can be swivelled by means of their respective separate adjusting system. Each adjusting system is arranged between an upper or a lower wall portion of the nozzle housing and the flaps and, in the process, acts upon a primary or a secondary flap.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.